Extrusion presses are known from the state of the art that comprise dummy blocks with which pressure can be transmitted onto the material that is to be extruded. As a rule, the dummy blocks are rotation-symmetrical and are accommodated in a holder that sheathes them during the extrusion process. As a rule, the dummy block is made of metal such as hot work steel.
During extrusion, the dummy block is subjected to a high compressive load and to a diameter enlargement, which are associated with stressing of the material. This stress causes wear and tear of the dummy block material. Moreover, the extrusion devices according to the state of the art entail the problem that, at the beginning of the extrusion process, air that is contained in the holder often cannot escape completely, and this has a detrimental effect on the material to be extruded.
Therefore, efforts are aimed at developing dummy blocks that involve the least possible material stress and that thus translate into a longer service life of the dummy block. For example, German patent DE 100 36 463 B4 discloses an advantageous dummy block and an extrusion device having such a dummy block, wherein the dummy block comprises a filler piece having a pressing surface with which a force can be exerted onto a material that is to be extruded. The filler piece is surrounded by a sealing ring whose inner diameter is dimensioned in such a way that the inner conical surface of the sealing ring and the outer conical surface of the filler piece form a first gap. Moreover, at least one radial gap, which widens conically from the inside towards the outside, runs between the filler piece and the sealing ring.
With an eye towards improving such a prior-art dummy block, it comprises various parts that, for instance, can also be configured in one piece in order to reduce the number of parts. Moreover, it would be desirable if the overall height of the dummy block could be reduced so as to reduce the total weight and thus facilitate the assembly and disassembly. However, this is not possible with the prior-art dummy blocks without severely impairing the functionality and service life of the dummy block.
Moreover, it would be advantageous if it were possible to remove and replace only the wearing parts of a dummy block via the front, without having to dismantle the entire construction. At the least the sealing ring and the filler piece can be viewed as wearing parts since they are highly stressed during operation in an extrusion press and which display wear and tear.
If one wants to replace only the filler piece and the sealing ring of the dummy block known from German patent DE 100 36 463 B4, however, it is necessary to completely dismantle several other parts before the filler piece and the sealing ring can be removed.
International patent application WO 98/03277 A1 describes a dummy block having a base part, a connecting element to connect the base part to an extrusion ram, a replaceable closing ring on a front area that surrounds the dummy block, as well as a device for detachably securing the closing ring to the base part. Moreover, the dummy block comprises a device for latching the billet container into the closing ring during the extrusion. The closing ring is made of metal and has a conical inner surface that converges towards the base part. The device for latching the billet container into the closing ring contains a metal extrusion ram with an end face having a conical surface, whereby the end face of the extrusion ram is pressed into the ring during the extrusion. The converging surfaces of the ring and the end face of the extrusion ram are at such a distance that the extrusion ram is prevented from entering the ring.
German utility model DE 73 14 414 U describes a dummy block for the extrusion rams of extruders, whereby the end face of the dummy block has a circular recess facing the material that is to be pressed, and it also has a conical seat surface for placement of an inner plate that, when it has been positioned, is flush with the end face of the dummy block.
Moreover, German patent application DE 41 32 810 A1 discloses a fixed dummy block for the extrusion ram of a metal extruder having a venting means. Due to the convex configuration of the side of the dummy block facing the material that is to be pressed, the air entrapped during the upsetting of the billet in the extrusion container can escape via the closing ring that has not yet spread as well as via the bores arranged in the spreading ring.